Maybe the designers are trying to discourage the use of tab characters by making the visible version annoying? :)

I think that if I ever worked anywhere that allowed tab characters in their source code, I would agree with you and wouldn’t be able to have visible whitespace turned on. As it is, however, I like seeing visible SPACE characters, and I actually have to INCREASE the default level of highlight for them using a Pythonscript command, because the default is just too weak.

Sorry but I don’t think there is an easy solution for you with the visible tab characters…